The invention relates to an electric rotary device of permanent magnet type, and more particularly relates to an improvement in the magnetic field structure of the electric rotary device of permanent magnet type such as an electric motor or an electric generator.
For convenience sake, FIGS. 1-4 are provided to explain the prior art in the field of the invention, in which a well known electric motor M is shown. The electric motor M is generally composed of a stator 1 and a rotor 2 which is rotatably mounted within the stator 1. The stator 1 consists of a cylindrical case 3 and a pair of permanent magnets 4,4 arranged opposite to each other and secured to the inner face of the case 3. The rotor 2 consists of an armature core 6 secured to the central rotation shaft 5 and a plurality of windings 7 wound around the arms 6b of the armature core 6. Thus the rotor 2 is rotated on the axis X-X in the direction R with the electric current flowing the armature windings 7.
According to the abovementioned old electric motor M, the permanent magnets 4,4 are each semicircular in the transverse section as shown in FIG. 2 and arranged around the central rotation shaft 5 with a configuration to be rectangular in the front elevational projection as shown in FIG. 3. It is therefore apparent that the magnetic flux of permanent magnets 4,4 is evenly distributed with respect to the rotating direction R of rotor 2. On the other hand, the distribution of the magnetic flux will abruptly change between the permanent magnets 4,4 during rotation of the rotor 2. As the result, the rotor 2 is shocked during each distribution of magnetic flux change, and is accordingly prevented from attaining a stabilized smooth rotation. It is apparent that such a property of the motor will have an adverse influence, for example, on a tape recorder which requires a high rotational precision for producing a natural phonetic sound.
In in order to eliminate the abovementioned defect of the electric motor, it has been proposed in the prior art to modify each of the front faces 6a of the armature core 6 into a parallelogramic shape in such a manner that a predetermined axial portion w of each face 6a may be varied in the rotating direction R of rotor 2, and then to wind each winding 7 around the armature core 6 in accordance to the parallelogramic shape of the face 6a as shown in FIG. 4.
In this case, however, it has been generally observed that the whole configuration of armature core 6 is considerably complicated and accordingly, it is difficult to produce such an armature core. As the result, the production of armature core 6 is deteriorated with an additional increase of production cost.
The present invention has been provided to eliminate the abovementioned defect of the prior art. It is therefore a primary object of the invention to smoothly vary the distribution of magnetic flux during rotation of the rotor of electric motor or electric generator to thereby operate the same in a smooth and stabilized condition without any rotational shocks due to the abrupt distribution change of magnetic flux.
It is another aspect of the invention to provide a new electric rotary device of permanent magnetic type attaining the abovementioned object with a simple structure adapted for mass production of the device.